25th International Meeting on Organic Geochemistry IMOG 2011

P-217
The Vinylguaiacol/Indole or VGI ("Veggie") Ratio: Assessing
Relative Contributions of Terrestrial and Aquatic Organic Matter
to Sediments
Michael Kruge, Kevin Olsen, Jaroslaw Slusarczyk, Elaine Gomez
Montclair State University, Montclair (NJ), United States of America (corresponding
author:krugem@mail.montclair.edu)
In studies of the organic matter (OM) fraction of
marine, estuarine, fluvial, or lacustrine sediments, one
of the most fundamental distinctions to be made is
that between terrestrial and aquatic OM. To
supplement the parameters commonly used for this
purpose (e.g., C/N and stable isotope ratios), we
proposed the Vinylguaiacol/Indole or VGI ("Veggie")
ratio, defined as [vinylguaiacol / (indole +
vinylguaiacol)] using data produced by analytical
pyrolysis-gas chromatography/mass spectrometry of
dried, homogenized sediment samples [1]. The ratio
employs the peak areas of these two compounds on
the mass chromatograms of their molecular ions (m/z
150 and 117, respectively). Major pyrolysis products
of terrestrial plant lignin include a variety of
methoxyphenols, notably 4-vinylguaiacol. In contrast,
aquatic algae and bacteria characteristically produce
distinctive organonitrogen compounds upon pyrolysis,
particularly indole, derived from the amino acid
tryptophan. The end member VGI ratio value of 1.00
is nearly obtained for reference land plant matter,
such as maple wood (Fig. 1d). The end member
value of 0.00 is obtained for cultured microbes,
including Escherichia coli (Fig. 1a). Vinylguaiacol and
indole are commonly detected in Recent sediment
pyrolysates. We hypothesized that their relative
quantities therein should be proportional to the
contributions of land plant and aquatic OM,
respectively [1]. While soil microbes in terrestrial OM
would lead to a diminution of VGI values, stable
isotope and C/N ratios would likely be similarly
perturbed.
Systematic variations in VGI ratio values are
observed among estuarine sediments from southern
New York and New England (USA). Samples taken
from Spartina peat marshes at the mouths of major
rivers entering Long Island Sound have high (> 0.8)
VGI ratio values. Jamaica Bay (New York), behind an
Atlantic barrier island and with marsh islands and
multiple urbanized tidal creeks, displays a very wide
VGI range (Fig. 1b,c), affected by proximity to stands
of marsh vegetation, bathymetry, and sediment grain
size. Sediments from New Haven (Connecticut)
harbour show a diminution in VGI values from 0.66 at
the mouth of a river in the innermost harbour to 0.08
at the harbour entrance over a distance of only 4 km,
as terrestrial influences wane moving towards open
water. In Long Island Sound, deep water sediments
show a strong predominance of aquatic OM (VGI
about 0.05), while nearshore sediments collected
close to the mouths of rivers have a greater terrestrial
OM component (VGI of 0.15 to 0.23). The results
demonstrate a precipitous decrease in the relative
amounts of unaltered land plant OM in the offshore
direction, but also that a minor fraction persists in
deeper water environments.
Figure 1. Partial summed m/z 117 + 150 mass
chromatograms of pyroysates of sediment samples
and reference biological materials. I: indole; VG:
vinylguaiacol. VGI ratio values are given for each.
[1] Micic et al., 2010, Org. Geochem. 41:971-974.
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